MODELING THE SURFACE-POTENTIAL AREA DEPENDENCE OF A STEARIC-ACID MONOLAYER

Based on a 3-layer capacitor approach used previously to describe the surface potential of condensed phase monolayers we have developed a model which appears to explain the main features of the surface potential area (DELTA-V-A) isotherm of stearic acid. The model suggests that a large reduction in the local permittivity in the neighbourhood of the headgroup dipoles from 78.4 to 6.5 is the cause of the rapid increase in DELTA-V when the monolayer is compressed below a critical area per molecule (A(c) congruent-to 30 angstrom2/molecule). We associate this with the growth of domains in the monolayer.